In a Gigabit-capable passive optical network (GPON) system, an optical line terminal (OLT) device located at a central office end may be connected to one or more optical network terminals (ONT) or optical network units (ONU) (For ease of description, an ONT is used for description below instead of an ONT and/or an ONU).
The GPON system is a time division multiplexing (TTDM) system. In a downlink direction, the OLT sends, by using an optical signal with a fixed frequency or wavelength, downlink information to all ONTs connected to the OLT, and each ONT may determine, according to its own identity information, information sent by the OLT to itself. In an uplink direction, each ONT emits light in a specific timeslot according to a rule of time division multiplexing uplink optical line bandwidth, that is, according to a scheduling mechanism of dynamic bandwidth allocation (DBA) of the OLT, so as to send uplink information to the OLT by using an optical light.
In the GPON system, transmit optical power and receiver sensitivity of an optical module vary according to different classes of optical modules. For example, for an OLT optical module of class B+ (CLASS B+), optical transmit power is 1.5 to 5 dBm, and receiver sensitivity is ≦−28 dBm. For this type of optical modules, if actual power of a received optical signal is less than −28 dBm, stable running of the system may be affected, which may cause bit errors or may even cause the system to be offline. Therefore, if the system can detect in time a value of the power of the optical signal actually received by the optical module, network robustness can be learned and a pre-warming can be given if necessary.
Likewise, line attenuation capabilities, which can be supported by a system having optical modules of different classes, of an optical distribution network (ODN) are different. For example, an optical module of class B+ (CLASS B+) can support maximum ODN line attenuation of 28 dB. That is, if ODN line attenuation exceeds 28 dB, stable running of the system may be affected, which may cause bit errors or may even cause the system to be offline. If the system can detect a degree of the ODN line attenuation in time, network robustness can be learned and a pre-warning can be given if necessary. A method for detecting actual ODN attenuation by a system is as follows: separately detect optical transmit power of the optical module of the OLT or ONT and optical power actually received by a peer (ONT or OLT) optical module, and calculate the power difference between them, so that ODN attenuation can be determined.
Therefore, it is very meaningful to detect in time actual transmit optical power and actually received optical power of an OLT and ONT optical module.
At present, to detect power of an uplink optical signal of a specific ONT received by an OLT, a triggering signal can be outputted when the specific ONT sends the uplink optical signal, where duration of the triggering signal is the same as duration for sending the uplink optical signal by the specific ONT, that is, the duration of the triggering signal is the same as uplink duration corresponding to uplink bandwidth of the uplink optical signal. The triggering signal is used to trigger a resistor capacitor (RC) circuit inside the OLT to perform charging, so as to detect the power of the uplink optical signal received by the OLT.
However, because uplink bandwidth of each uplink optical signal may be different, accuracy and repeatability for measuring power of an uplink optical signal may be relatively poor.